Provided by: iputils-ping_20121221-4ubuntu1.1_amd64 
NAME
ping, ping6 - send ICMP ECHO_REQUEST to network hosts
SYNOPSIS
ping [-aAbBdDfhLnOqrRUvV] [-c count] [-F flowlabel] [-i interval] [-I interface] [-l preload] [-m mark]
[-M pmtudisc_option] [-N nodeinfo_option] [-w deadline] [-W timeout] [-p pattern] [-Q tos] [-s
packetsize] [-S sndbuf] [-t ttl] [-T timestamp option] [hop ...] destination
DESCRIPTION
ping uses the ICMP protocol's mandatory ECHO_REQUEST datagram to elicit an ICMP ECHO_RESPONSE from a host
or gateway. ECHO_REQUEST datagrams (``pings'') have an IP and ICMP header, followed by a struct timeval
and then an arbitrary number of ``pad'' bytes used to fill out the packet.
ping6 is IPv6 version of ping, and can also send Node Information Queries (RFC4620). Intermediate hops
may not be allowed, because IPv6 source routing was deprecated (RFC5095).
OPTIONS
-a Audible ping.
-A Adaptive ping. Interpacket interval adapts to round-trip time, so that effectively not more than
one (or more, if preload is set) unanswered probe is present in the network. Minimal interval is
200msec for not super-user. On networks with low rtt this mode is essentially equivalent to flood
mode.
-b Allow pinging a broadcast address.
-B Do not allow ping to change source address of probes. The address is bound to one selected when
ping starts.
-c count
Stop after sending count ECHO_REQUEST packets. With deadline option, ping waits for count
ECHO_REPLY packets, until the timeout expires.
-d Set the SO_DEBUG option on the socket being used. Essentially, this socket option is not used by
Linux kernel.
-D Print timestamp (unix time + microseconds as in gettimeofday) before each line.
-f Flood ping. For every ECHO_REQUEST sent a period ``.'' is printed, while for ever ECHO_REPLY
received a backspace is printed. This provides a rapid display of how many packets are being
dropped. If interval is not given, it sets interval to zero and outputs packets as fast as they
come back or one hundred times per second, whichever is more. Only the super-user may use this
option with zero interval.
-F flow label
ping6 only. Allocate and set 20 bit flow label (in hex) on echo request packets. If value is
zero, kernel allocates random flow label.
-h Show help.
-i interval
Wait interval seconds between sending each packet. The default is to wait for one second between
each packet normally, or not to wait in flood mode. Only super-user may set interval to values
less 0.2 seconds.
-I interface
interface is either an address, or an interface name. If interface is an address, it sets source
address to specified interface address. If interface in an interface name, it sets source
interface to specified interface. For ping6, when doing ping to a link-local scope address, link
specification (by the '%'-notation in destination, or by this option) is required.
-l preload
If preload is specified, ping sends that many packets not waiting for reply. Only the super-user
may select preload more than 3.
-L Suppress loopback of multicast packets. This flag only applies if the ping destination is a
multicast address.
-m mark
use mark to tag the packets going out. This is useful for variety of reasons within the kernel
such as using policy routing to select specific outbound processing.
-M pmtudisc_opt
Select Path MTU Discovery strategy. pmtudisc_option may be either do (prohibit fragmentation,
even local one), want (do PMTU discovery, fragment locally when packet size is large), or dont (do
not set DF flag).
-N nodeinfo_option
ping6 only. Send ICMPv6 Node Information Queries (RFC4620), instead of Echo Request.
help Show help for NI support.
name Queries for Node Names.
ipv6 Queries for IPv6 Addresses. There are several IPv6 specific flags.
ipv6-global
Request IPv6 global-scope addresses.
ipv6-sitelocal
Request IPv6 site-local addresses.
ipv6-linklocal
Request IPv6 link-local addresses.
ipv6-all
Request IPv6 addresses on other interfaces.
ipv4 Queries for IPv4 Addresses. There is one IPv4 specific flag.
ipv4-all
Request IPv4 addresses on other interfaces.
subject-ipv6=ipv6addr
IPv6 subject address.
subject-ipv4=ipv4addr
IPv4 subject address.
subject-name=nodename
Subject name. If it contains more than one dot, fully-qualified domain name is assumed.
subject-fqdn=nodename
Subject name. Fully-qualified domain name is always assumed.
-n Numeric output only. No attempt will be made to lookup symbolic names for host addresses.
-O Report outstanding ICMP ECHO reply before sending next packet. This is useful together with the
timestamp -D to log output to a diagnostic file and search for missing answers.
-p pattern
You may specify up to 16 ``pad'' bytes to fill out the packet you send. This is useful for
diagnosing data-dependent problems in a network. For example, -p ff will cause the sent packet to
be filled with all ones.
-q Quiet output. Nothing is displayed except the summary lines at startup time and when finished.
-Q tos Set Quality of Service -related bits in ICMP datagrams. tos can be decimal (ping only) or hex
number.
In RFC2474, these fields are interpreted as 8-bit Differentiated Services (DS), consisting of:
bits 0-1 (2 lowest bits) of separate data, and bits 2-7 (highest 6 bits) of Differentiated
Services Codepoint (DSCP). In RFC2481 and RFC3168, bits 0-1 are used for ECN.
Historically (RFC1349, obsoleted by RFC2474), these were interpreted as: bit 0 (lowest bit) for
reserved (currently being redefined as congestion control), 1-4 for Type of Service and bits 5-7
(highest bits) for Precedence.
-r Bypass the normal routing tables and send directly to a host on an attached interface. If the
host is not on a directly-attached network, an error is returned. This option can be used to ping
a local host through an interface that has no route through it provided the option -I is also
used.
-R ping only. Record route. Includes the RECORD_ROUTE option in the ECHO_REQUEST packet and
displays the route buffer on returned packets. Note that the IP header is only large enough for
nine such routes. Many hosts ignore or discard this option.
-s packetsize
Specifies the number of data bytes to be sent. The default is 56, which translates into 64 ICMP
data bytes when combined with the 8 bytes of ICMP header data.
-S sndbuf
Set socket sndbuf. If not specified, it is selected to buffer not more than one packet.
-t ttl ping only. Set the IP Time to Live.
-T timestamp option
Set special IP timestamp options. timestamp option may be either tsonly (only timestamps),
tsandaddr (timestamps and addresses) or tsprespec host1 [host2 [host3 [host4]]] (timestamp
prespecified hops).
-U Print full user-to-user latency (the old behaviour). Normally ping prints network round trip time,
which can be different f.e. due to DNS failures.
-v Verbose output.
-V Show version and exit.
-w deadline
Specify a timeout, in seconds, before ping exits regardless of how many packets have been sent or
received. In this case ping does not stop after count packet are sent, it waits either for
deadline expire or until count probes are answered or for some error notification from network.
-W timeout
Time to wait for a response, in seconds. The option affects only timeout in absence of any
responses, otherwise ping waits for two RTTs.
When using ping for fault isolation, it should first be run on the local host, to verify that the local
network interface is up and running. Then, hosts and gateways further and further away should be
``pinged''. Round-trip times and packet loss statistics are computed. If duplicate packets are received,
they are not included in the packet loss calculation, although the round trip time of these packets is
used in calculating the minimum/average/maximum round-trip time numbers. When the specified number of
packets have been sent (and received) or if the program is terminated with a SIGINT, a brief summary is
displayed. Shorter current statistics can be obtained without termination of process with signal SIGQUIT.
If ping does not receive any reply packets at all it will exit with code 1. If a packet count and
deadline are both specified, and fewer than count packets are received by the time the deadline has
arrived, it will also exit with code 1. On other error it exits with code 2. Otherwise it exits with
code 0. This makes it possible to use the exit code to see if a host is alive or not.
This program is intended for use in network testing, measurement and management. Because of the load it
can impose on the network, it is unwise to use ping during normal operations or from automated scripts.
ICMP PACKET DETAILS
An IP header without options is 20 bytes. An ICMP ECHO_REQUEST packet contains an additional 8 bytes
worth of ICMP header followed by an arbitrary amount of data. When a packetsize is given, this indicated
the size of this extra piece of data (the default is 56). Thus the amount of data received inside of an
IP packet of type ICMP ECHO_REPLY will always be 8 bytes more than the requested data space (the ICMP
header).
If the data space is at least of size of struct timeval ping uses the beginning bytes of this space to
include a timestamp which it uses in the computation of round trip times. If the data space is shorter,
no round trip times are given.
DUPLICATE AND DAMAGED PACKETS
ping will report duplicate and damaged packets. Duplicate packets should never occur, and seem to be
caused by inappropriate link-level retransmissions. Duplicates may occur in many situations and are
rarely (if ever) a good sign, although the presence of low levels of duplicates may not always be cause
for alarm.
Damaged packets are obviously serious cause for alarm and often indicate broken hardware somewhere in the
ping packet's path (in the network or in the hosts).
TRYING DIFFERENT DATA PATTERNS
The (inter)network layer should never treat packets differently depending on the data contained in the
data portion. Unfortunately, data-dependent problems have been known to sneak into networks and remain
undetected for long periods of time. In many cases the particular pattern that will have problems is
something that doesn't have sufficient ``transitions'', such as all ones or all zeros, or a pattern right
at the edge, such as almost all zeros. It isn't necessarily enough to specify a data pattern of all
zeros (for example) on the command line because the pattern that is of interest is at the data link
level, and the relationship between what you type and what the controllers transmit can be complicated.
This means that if you have a data-dependent problem you will probably have to do a lot of testing to
find it. If you are lucky, you may manage to find a file that either can't be sent across your network
or that takes much longer to transfer than other similar length files. You can then examine this file
for repeated patterns that you can test using the -p option of ping.
TTL DETAILS
The TTL value of an IP packet represents the maximum number of IP routers that the packet can go through
before being thrown away. In current practice you can expect each router in the Internet to decrement
the TTL field by exactly one.
The TCP/IP specification states that the TTL field for TCP packets should be set to 60, but many systems
use smaller values (4.3 BSD uses 30, 4.2 used 15).
The maximum possible value of this field is 255, and most Unix systems set the TTL field of ICMP
ECHO_REQUEST packets to 255. This is why you will find you can ``ping'' some hosts, but not reach them
with telnet(1) or ftp(1).
In normal operation ping prints the TTL value from the packet it receives. When a remote system receives
a ping packet, it can do one of three things with the TTL field in its response:
• Not change it; this is what Berkeley Unix systems did before the 4.3BSD Tahoe release. In this case the
TTL value in the received packet will be 255 minus the number of routers in the round-trip path.
• Set it to 255; this is what current Berkeley Unix systems do. In this case the TTL value in the
received packet will be 255 minus the number of routers in the path from the remote system to the
pinging host.
• Set it to some other value. Some machines use the same value for ICMP packets that they use for TCP
packets, for example either 30 or 60. Others may use completely wild values.
BUGS
• Many Hosts and Gateways ignore the RECORD_ROUTE option.
• The maximum IP header length is too small for options like RECORD_ROUTE to be completely useful.
There's not much that that can be done about this, however.
• Flood pinging is not recommended in general, and flood pinging the broadcast address should only be
done under very controlled conditions.
SEE ALSO
netstat(1), ifconfig(8).
HISTORY
The ping command appeared in 4.3BSD.
The version described here is its descendant specific to Linux.
SECURITY
ping requires CAP_NET_RAW capability to be executed. It may be used as set-uid root.
AVAILABILITY
ping is part of iputils package and the latest versions are available in source form at
http://www.skbuff.net/iputils/iputils-current.tar.bz2.